This application is base upon European Application Serial Number 00400815,7 filed on Mar. 23, 2000, from which the benefit of priority is hereby claimed, and the full content which is incorporated herein by reference as though fully set forth.
1. Field of the Invention
The present invention generally relates to an apparatus for localized heating of optical fibers, and more particularly to an apparatus and method for splicing optical fibers. The present invention also relates to an apparatus for controlling the intensity of a laser beam.
2. Technical Background
Manufacturers and assemblers of optical networks, systems, and components often must splice two optical fibers together. This is typically accomplished by aligning and fusing the ends of the fibers.
FIG. 1 shows an electric splicer commonly used to splice the ends 14a and 14bof two fibers 12a and 12b together. Support members 20a and 20b support fibers 12a and 12b such that the fibers are aligned and the two ends abut one another. Fibers 12a and 12b extend from support members 20a and 20b in a cantilevered fashion with the ends of the fibers positioned equidistant from the support members by a distance a. A pair of electrodes 16a and 16b are provided on opposite sides of the splicing area 15 with their tips 18a and 18b, respectively, aligned along an axis that extends through the center of the splicing region 15. Then, by creating an electric arc between electrode tips 18a and 18b, the electric arc heats the ends 14a and 14b of the fibers above the melting point of the fibers to fuse the ends of the fibers together.
In the arrangement shown in FIG. 1, the cantilever distance a must be at least 3 mm to prevent the electric arc produced by the electrodes 16a and 16b from straying and reaching one of support members 20a or 20b. A cantilever distance a of 3 mm causes problems since this distance is about 24 times the diameter of the typical fiber (125 xcexcm ). This relatively large cantilever distance allows ends 14a and 14b to sag, which makes it very difficult to properly align the two ends 14a and 14b. Also contributing to alignment problems is the intrinsic curl that most fibers exhibit. This intrinsic curl is typically about 4 meters in radius. Also, when the fiber ends are pushed together, the fibers are more likely to flex with the larger cantilever distance and thereby cause misalignment. On average, such transverse misalignment of the fiber ends results in a 1 dB loss in the signals propagating through the spliced area.
Another difficulty in utilizing an electric splicer is in the control and maintenance of the electric arc in a small space with a predetermined and constant intensity. The localization and intensity of the electric arc at the splicing area is affected by numerous parameters including air pressure, hygrometry dependence of the electric arc, erosion of the electrode point, and dust and fiber particles on the electrodes.
Because of the above-noted problems experienced when utilizing an electric splicer, there exists a need for a fiber splicing apparatus that allows accurate and consistent splicing.
While CO2 lasers have been utilized previously to heat portions of fibers to produce diffraction gratings and the like, the manner by which such CO2 lasers were controlled is not sufficient to control a CO2 laser to splice together the ends of two fibers. Specifically, when splicing optical fibers, the intensity of the laser beam is preferably maintained at a constant level to provide the appropriate energy density in splicing area 115. In the past, the intensity of CO2 lasers has been controlled by monitoring the intensity level of the beam and by varying the duty cycle of the electrical power signal used to power the CO2 laser. More specifically, a portion of the laser beam is split and provided to a thermo-pile detector that produces a voltage level corresponding to the intensity of the impinging laser beam. The voltage level generated by the detector is compared against a reference and used to regulate the duty cycle using pulse width modulation to thereby vary the voltage applied to an internal RF amplifier stage that controls the RF drive applied to the laser electrodes. Although CO2 lasers are generally quite stable after an initial heating period, the intensity control system described above tends to destabilize the laser output by repeatedly undercompensating and then overcompensating the laser.
A CO2 laser controlled using the above control system exhibits a random behavior in the range of xc2x12 percent of the total laser power. Knowing that the energy quantity is given by: xcex94Q=Pxcex94t=mCPxcex94T, where P is the energy on the fiber, xcex94t is the pulse duration, m is the fiber weight, Cp is the heat capacity which is 1200 J/kg/xc2x0C. and xcex94T is the temperature difference. Thus,       Δ    ⁢          xe2x80x83        ⁢    T    =                    P        ⁢                  xe2x80x83                ⁢        Δ        ⁢                  xe2x80x83                ⁢        t                    mC        p              .  
Therefore, a xc2x12 percent variation in power P induces a xc2x12 percent variation in temperature at the splicing area. The temperature during the splice is about 1800xc2x0 C. which is the melting temperature of the fiber. Thus, a xc2x12 percent variation in temperature leads to xc2x136xc2x0 C. of temperature variation. Such a variation causes unacceptable inconsistencies during the fiber-splicing process.
Accordingly, it is an aspect of the present invention to solve the above problems by providing a splicing apparatus that allows the reduction of the cantilever distance of the fibers. It is another aspect of the present invention to provide a splicing apparatus having a stable splicing temperature thereby providing consistent spliced fiber characteristics. Another aspect of the invention is to provide a splicing apparatus that does not suffer from the problems associated with cleaning of electrodes.
To achieve these and other aspects and advantages, the splicing apparatus of the present invention comprises a support for supporting the two optical fibers such that the ends thereof are aligned and in physical contact. The splicing apparatus further includes a laser for projecting a laser beam onto the ends of the optical fibers to heat and thereby fuse together the ends of the fibers.
According to another embodiment, an apparatus is provided for heating a region of one or more optical fibers. The apparatus comprises a laser for producing a laser beam, and an optical modulator positioned to receive and selectively modulate the intensity of the laser beam to project a modulated laser beam along a first optical path that is directed to the ends of the optical fiber(s) to be heated. The apparatus further includes a control loop to monitor the intensity of the modulated laser beam and control the optical modulator to thereby regulate the intensity of the modulated laser in response to the monitored intensity level.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the following description together with reference to the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description serve to explain the principals and operation of the invention.